Much of motor skill research, understandably, examines motor skill acquisition during the learning experience. New findings suggest that a wealth of changes that occur outside the learning experience. Particularly, performance may actually improve after a delay, or "off-line". Interestingly, though, these off-line effects differ between motor skills. I hypothesize that recruitment of the declarative system during the task, a component that has been generally neglected in motor control studies, has a strong influence on the patterns of forgetting or improvement between sessions. Consistent with this hypothesis, I present preliminary evidence that patients with impairment of the declarative memory system, including patient HM, show less forgetting in a reach adaptation task with passage of time than healthy controls. Further, in sequence learning, recruitment of the declarative system after acquisition leads to delayed gains, possibly by impairing the mechanism that would otherwise prohibit off-line gains. Finally, sleep deprivation does not impair retention on a reaching task, possibly because sleep deprivation is known to impair declarative processes. Systematic manipulation of declarative recruitment during reaching task should shed light on mechanisms underlying the post-acquisition learning process. In Study 1,1 will administer post-training declarative task or a control task immediately after training on the reaching task and assess effects on later retention. In Study 2, some participants will perform a secondary memory task concurrently with the reaching task;others will perform the reaching task only. Effects on retention after a delay will be assessed. In Study 3,1 will explore declarative learning and potential retention effects related to the rate of introduction of a perturbing force field (gradually or suddenly) during the reaching task. In Study 3,1 will explore the effect of sleep deprivation on declarative learning and retention. In Study 5,1 will explore patterns of retention in patients with declarative impairment and healthy controls. This research is of importance in rehabilitation research. Practitioners seek the most efficient rehabilitation possible. By capitalizing on "off-line" gains in performance, we may develop optimal rehabilitation strategies. The current research examines factors that possibly encourage off-line gains.